The present invention relates to an actuator for converting rotational movement to linear movement and more specifically to an actuator that transmits a predetermined limited linear force.
Compact backlash free systems for converting a rotational movement to an accurate linear movement are known. Such devices are used, for example, for controlling the size of an opening through which material is metered. In a paper machine, for example, there is a requirement to vary the size of the individual transverse openings across the face of the machine for feeding fibre suspension from the slice of the machine. A short section of the slice lip is moved precisely by a motor driven actuator and this movement or deflection of the slice lip requires a specific force. Too great a force causes too great a deflection and insufficient force does not provide sufficient movement.
One example of a slice lip automation device is shown in our U.S. Pat. No. 4,833,941. This patent illustrates two stages of harmonic drive wave generators in the drawings, although if sufficient reduction can be achieved in a single stage harmonic drive gear, the actuator performs satisfactorily. The disclosure of this patent is incorporated herein by reference.
A slice lip actuator is a compact unit and converts a relatively high speed rotational movement of relatively low torque into an accurate linear movement to provide a relatively high output force. A high speed low torque motor drives a backlash free gear reducer which in turn rotates a drive nut. The drive nut drives an output shaft, which is restricted from rotating, to move the shaft linearly.